1. Field of the Invention
The present invention relates generally to anemometers and, more specifically, to a thermal remote anemometer system.
2. Description of Related Art
Wind tunnel testing has become increasingly more important over the years. The increase in such testing has brought an increasing need to control and measure the flow characteristics of the tunnels and models. For example, the flow may need to be altered to minimize shock waves; or the flow may need to be reduced from a supersonic mode to a subsonic mode. To be able to provide specific characterization to the flow, it is necessary to have the ability to accurately measure the flow characteristics.
In the past, gas flow characterization has been accomplished by mechanical and thermal devices. One typical mechanical device is a rotating anemometer such as a wind cup or windmill device that relates its rotational speed to the flow. One drawback to these devices is that they only measure a swept volume which may not necessarily be clearly indicative of the flow adjacent a test model. Other drawbacks are their flow speed limitations and size restrictions.
Thermal anemometer devices have included the hot-wire type. Those hot-wire devices supply a measured current to the tip of the sensor. A change in current is a measure of the heat transferred away from the sensor, which is an indication of the flow over the sensor. Some problems associated with the hot-wire type device are that holes may have to be drilled in the test models, wires must be run internally of the model and brought out of a wind tunnel for measurement, and the model must be refinished to remove artifacts. If the model is not properly refinished, artifacts may interact with the flow and thereby affect the reliability of the measurements. The point measurements provided by hot-wire devices are also undesirable due to their fixed location and inability to scan.
Artisans have attempted to provide remote measurement devices, but these typically only measure temperature of an object rather than providing characteristics of a flow around a model. These are found, for example, in Wickersheim, "Optical Temperature Measurement Technique Utilizing Phosphors," U.S. Pat. No. 4,075,493; Quick et al., "Fiber Optic Temperature Sensor," U.S. Pat. No. 4,223,226; and Bernal, "Gas Temperature Measurement System Employing A Laser," U.S. Pat. No. 3,632,212.
A need still exists in the art to provide an anemometer system that can accurately characterize a flow over a model, such as one in a wind tunnel, in a remote, non-contact and passive fashion.